Sio2-layered double hydroxide microspheres and their use as catalyst supports in ethylene polymerisation

ABSTRACT

A catalyst system is provided which comprises a solid support material having, on its surface, one or more catalytic transition metal complex wherein the solid support material comprises SiO 2 @AMO-LDH microspheres having the formula I: (i) wherein, M z+  and M′ y+  are two different charged metal cations; z=1 or 2; y=3 or 4; 0&lt;x&lt;0.9; b is 0 to 10; c is 0.01 to 10, preferably &gt;0.01 and &lt;10; p&gt;0 q&gt;0; X n−  is an anion with n&gt;0, preferably 1−5a=z(1−x)+xy−2; and the AMO-solvent is an 100% aqueous miscible organic solvent. Preferably, M′ in the formula I is Al. Preferably, M in the formula I is Li, Mg or Ca. The catalyst system has use in the polymerisation and/or copolymerisation of at least one olefm to produce a homopolymer and/or copolymer.

The present invention relates to SiO₂-layered double hydroxide (LDH)core-shell microspheres and to their use as catalyst supports inethylene polymerisation.

Core shell particles are described in the literature by “core@shell”(for example by Teng et al., Nano Letters, 2003, 3, 261-264, or by“core/shell” (for example J. Am. Chem Soc., 2001, 123, pages 7961-7962).We have adopted the “core@shell” nomenclature as it is emerging as themore commonly accepted abbreviation.

A silica-layered double hydroxide microsphere is known to comprise asilica microsphere having solid LDH attached to its surface. Such amaterial, denoted as SiO₂@LDH, may be a core-shell material where theSiO₂ microsphere is a solid sphere, a yolk-shell material where the SiO₂microsphere comprises an outer shell and a smaller SiO₂ sphere containedwithin the outer shell wherein there is a hollow portion between thesmaller sphere and the inner surface of the outer shell, or a hollowshell material wherein the SiO₂ microsphere has a hollow interior.

Layered double hydroxides (LDHs) are a class of compounds which comprisetwo or more metal cations and have a layered structure. A review of LDHsis provided in Structure and Bonding; Vol. 119, 2005 Layered DoubleHydroxides ed. X Duan and D.G. Evans. The hydrotalcites, perhaps themost well-known examples of LDHs, have been studied for many years. LDHscan intercalate anions between the layers of the structure.

LDHs have captured much attention in recent years due to their impactacross a range of applications, including catalysis, optics, medicalscience and in inorganic-organic nanocomposites. A new family ofdispersible, hydrophobic LDHs using an aqueous miscible organic solventtreatment (AMOST) method has been synthesized. These, so called,AMO-LDHs may exhibit surface areas in excess of 400 m²g⁻¹ and porevolumes in excess of 2.15 cc g⁻¹, which is nearly two orders ofmagnitude higher than conventional LDHs. AMO-LDHs have a unique chemicalcomposition, which may be defined by the formula A

[M^(z+) _(1−x)M′^(y+)×(OH₂]¹⁺(A^(n−))_(a/n)·bH₂O·c(AMO-solvent)   (A),

where M^(z+) and M′^(y+) are metal cations or mixtures of metal cations,z is 1 or 2; and y is 3 or 4, 0<x<1, b=0−10, c=0.01−10, A is a chargecompensating anion, n, n>0 (typically 1-5) and a=z(1−x)+xy−2.AMO-solvents are those which are 100% miscible in water. Typically, theAMO-solvent is ethanol, acetone or methanol.

SiO₂@LDH microspheres are described by Shao et al, Chem. Mater. 2012,24, pages 1192-1197. Prior to treatment with a metal precursor solution,the SiO₂ microspheres are primed by dispersing them in an Al OOH primersol for two hours with vigorous agitation followed by centrifuging,washing with ethanol and drying in air for 30 minutes. This primingtreatment of the SiO₂ microspheres was repeated 10 times before the SiO₂spheres thus coated with a thin Al(OOH) film were autoclaved at 100° C.for 48 hours in a solution of Ni(NO₃)₂·6H₂O and urea. HollowSiO₂@NiAl-LDH microspheres obtained by this process were reported asexhibiting excellent pseudocapacitance performance.

Chen et al, J. Mater. Chem. A, 1, 3877-3880 describes the synthesis ofSiO₂@MgAl-LDHs having use in the removal of pharmaceutical pollutantsfrom water.

Polyethylene is the most widely used polyolefin with a global productionin 2011 of over 75 million tons per year. Innovation in both thesynthesis and the properties of polyethylene is still at the forefrontin both industry and academia. It is now more than thirty years sincethe first discoveries of highly active homogeneous catalysts for olefinpolymerisation. Since then, intensive research has led to greatercontrol over polymerisation activity and polymer structure than cangenerally be obtained with the original type of heterogeneousZiegler-Natta catalysts. Many different supports (e.g. SiO₂, Al₂O₃,MgCl₂ and clays) and immobilisation procedures have been investigated.

The object of the present invention is to provide novel catalyst systemsovercoming drawbacks of the prior art, in particular comprising novelsupports for heterogeneous ethylene polymerisation and novel ethylenepolymerisation catalyst systems comprising a supported catalyst.

This object is achieved by a catalyst system comprising a solid supportmaterial having, on its surface, one or more catalytic transition metalcomplex wherein the solid support material comprises SiO₂@AMO-LDHmicrospheres having the formula I

(SiO₂)_(p)@{[M^(z+) _((1−x))M′^(y+)_(x)(OH)₂]¹⁺(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (I)

wherein,

-   M^(z+) and M′^(y+) are two different charged metal cations;-   z=1 or 2;-   y=3 or 4;-   0<x<0.9;-   b is 0 to 10;-   c is 0.01 to 10;-   p>0-   q>0;-   X^(n−) is an anion with n>0, preferably 1-5-   a=z(1−x)+xy−2; and-   the AMO-solvent is an 100% aqueous miscible organic solvent.

It is preferred that the solid support material has the formula I inwhich M′ is Al.

It is further preferred that the solid support material has the formulaI in which M is Li, Mg or Ca.

Most preferred, the solid support material has the formula I in whichX^(n−) is selected from CO₃ ²⁻, OH⁻, F⁻, Cl⁻, Br, I⁻, SO₄ ²⁻, NO₃ ⁻ andPO₄ ³⁻, preferably CO₃ ²⁻, Cl⁻ and NO₃, or mixtures thereof.

Also preferred is that the solid support material has the formula I inwhich M is Mg, M′ is Al and X^(n−) is CO³⁻.

Preferably, the solid support material has the formula I in whichAMO-solvent is ethanol, acetone and/or methanol, preferably ethanol oracetone.

More preferably, the catalytic transition metal complex is at least onecomplex of a metal selected from zirconium, iron, chromium, cobalt,nickel, titanium and hafnium, the complex containing one or morearomatic or heteroaromatic ligands.

It is further preferred that the catalytic transition metal complex is ametallocene containing zirconium or hafnium.

It is most preferred that the catalytic transition metal complex is atleast one compound selected from

In a preferred embodiment, the system is obtainable by a processcomprising the step of activating the solid support material with analkylaluminoxane or triisobutylaluminium (TIBA), triethylaluminium (TEA)or diethylaluminium chloride (DEAC).

In a further preferred embodiment, the alkylaluminoxane ismethylaluminoxane (MAO) or modified methylaluminoxane (MMAO).

A further object is achieved by a method of making the catalyst systemwhich comprises

-   -   (a) providing a solid support material comprising SiO₂@AMO-LDH        microspheres having the formula (I)

(SiO₂)_(p)@{[M^(z+) _((1−x))M′^(y+)_(x)(OH)₂]^(a+)(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (I)

wherein,

M^(z+) and M′^(y+) are two different charged metal cations;

z=1 or 2;

y=3 or 4;

0<x<0.9;

b is 0 to 10;

c is 0.01 to10;

p>0,

q>0;

X^(n−) is an anion with n>0, preferably 1-5

a=z(1−x)+xy−2; and

the AMO-solvent is an aqueous miscible organic solvent,

-   -   (b) treating the SiO₂@AMO-LDH microspheres with at least one        catalytic transition metal complex having olefin polymerisation        catalytic activity.    -   Preferably, the solid support material has the formula I in        which M′ is Al.

More preferably, the solid support material has the formula I in which Mis Li, Mg or Ca or mixtures thereof.

Most preferably, the solid support material has the formula I in whichX^(n−) is selected from CO₃ ²⁻, OH⁻, F⁻, Cl⁻, Br, I⁻, SO₄ ²⁻, NO₃− andPO₄ ³⁻, preferably CO₃ ²⁻, Cl⁻ and NO₃−, or mixtures thereof.

It is preferred that the solid support material has the formula I inwhich M is Mg, M′ is Al and X^(n−) is CO₃ ⁻.

It is further preferred that c, in the formula I for the solid supportmaterial is >0 and AMO-solvent is acetone and/or ethanol, preferablyacetone or ethanol.

In a more preferred embodiment, the catalytic transition metal complexis at least one complex of a metal selected from zirconium, iron,chromium, cobalt, nickel, titanium and hafnium, the complex containingone or more aromatic or heteroaromatic ligands.

It is preferred that the catalytic transition metal complex is ametallocene containing zirconium or hafnium.

It is further preferred that the catalytic transition metal complex isat least one compound selected from

In a further embodiment, the method further comprises a step ofcalcining the SiO₂@AMO-LDH microspheres, before the treating step (b).

In a further embodiment, the method further comprises a step of treatingthe calcined SiO₂@AMO-LDH with an alkylaluminoxane before the treatingstep (b).

It is preferred that the alkylaluminoxane is methylaluminoxane (MAO) ormodified methylaluminoxane (MMAO).

According to a further aspect of the invention, there is provided acatalyst system, as defined herein, obtained, directly obtained orobtainable by a process defined herein.

The object is further achieved by the use of the inventive catalystsystem as a catalyst in the polymerisation and/or copolymerisation of atleast one olefin to produce a homopolymer and/or co-polymer.

Preferably, the olefin is ethylene.

More preferably, the copolymer comprises 1-10 wt % of a (4-8C) α-olefin.

Moreover, the object is achieved by a process for forming a polyethylenehomopolymer or a polyethylene copolymer which comprises reacting olefinmonomers in the presence of the inventive catalyst system.

The object is also achieved by a process for producing a polymer of anolefin which comprises contacting the olefin with the inventive solidcatalyst system.

Most preferred, the olefin is ethylene.

Finally, it is preferred that the process is performed at a temperatureof 60 to 100° C., preferably 70 to 80° C.

A silica-layered double hydroxide microsphere is known to comprise asilica microsphere having solid AMO-LDH attached to its surface. Such amaterial, denoted as SiO₂@AMO-LDH, may be a core-shell material wherethe SiO₂ microsphere is a solid sphere, a yolk-shell material where theSiO₂ microsphere comprises an outer shell and a smaller SiO₂ spherecontained within the outer shell wherein there is a hollow portionbetween the smaller sphere and the inner surface of the outer shell, ora hollow shell material wherein the SiO₂ microsphere has a hollowinterior.

The SiO₂ microspheres used in the preparation of the SiO₂@AMO-LDHmicrospheres used as the solid support material may be solid, yolk-shellor hollow microspheres and are commercially-available in a variety ofsizes (diameters). They can be prepared easily and quickly and atrelatively low cost. In addition, the silica microspheres are negativelycharged, which compliments the positive charged surface of AMO-LDHs,allowing for additive-free binding of the AMO-LDH by electrostaticinteractions. Most importantly, the silica spheres can be prepared sothat they are monodispersed, preventing aggregation of the AMO-LDHnanosheets. SiO₂ microspheres may be prepared by the Stöber process orby seeded growth, providing different levels of control over theparticle size. In the Examples, provided herein, three sizes of silicaspheres were synthesised, 300 nm, 550 nm and 800 nm.

In an embodiment, the silica microspheres do not contain any iron. In anembodiment, the silica microspheres comprise greater than 75% w/wSiO_(2.) Suitably, silica microspheres comprise greater than 85% w/wSiO₂. More suitably, the silica microspheres comprise greater than 95%w/w SiO₂. Most suitably, the silica microspheres comprise greater than98% w/w SiO_(2.)

In another embodiment, the silica microspheres consist essentially ofSiO₂.

In another embodiment, the silica microspheres consist of SiO₂.

In another embodiment, the SiO₂ microspheres have a diameter of between0.15 μm and 8 μm. Suitably, the SiO₂ microspheres have a diameter ofbetween 0.15 μm and 2 μm. More suitably, the SiO₂ microspheres have adiameter of between 0.15 μm and 1 μm. Most suitably, the SiO₂microspheres have a diameter of between 0.2 μm and 0.8 μm

The SiO₂@AMO-LDHs used as the solid support material in the catalystsystem of the invention has the formula I

(SiO₂)_(p)@{[M^(z+) _((1−x))M′^(y+)_(x)(OH)₂]^(a+)(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (I)

wherein,

-   M^(z+) and M′^(y+) are two different charged metal cations;-   z=1 or 2;-   y=3 or 4;-   0<x<0.9;-   b is 0 to 10;-   c is 0.01 to 10, preferably c>0.01 and <10;-   p>0,-   q>0;-   X^(n−) is an anion;-   n is the charge on the anion, n>0 (typically 1-5);-   a=z(1−x)+xy−2; and-   AMO-solvent is an aqueous miscible organic solvent.

These materials are made by a method which comprises the steps:

-   (a) contacting silica microspheres within a metal ion containing    solution containing metal ions M^(z+) and M′^(y+) and anion X^(n+)    in the presence of a base;-   (b) collecting the product; and-   (c) treating the product with AMO-solvent and recovering the solvent    treated material.

As stated above, M^(z+) and M′^(y+) are different charged metal cations.Having regard to the fact that z=1 or 2, M will be either a monovalentmetal cation or a divalent metal cation. When z=1, M is either a singlemonovalent metal cation or two or more different monovalent metalcations. When z=2, M is either a single divalent metal cation or two ormore different divalent metal cations. In an embodiment, z=2, i.e. M isone or more divalent metal cations. M′, in view of the fact that y=3 or4, will be a trivalent metal cation or a tetravalent metal cation. Whenz=3, M′ is either a single trivalent metal cation or two or moredifferent trivalent metal cations. When z=4, M′ is either a singletetravalent metal cation or two or more different tetravalent metalcations. In an embodiment, y=3, i.e. M′ is one or more trivalent metalcations.

A preferred example of a monovalent metal, for M, is Li. Examples ofdivalent metals, for M, include Ca, Mg, Zn, Fe and Ni and mixtures oftwo or more of these. Preferably, the divalent metal, if present, is Caor Mg. Examples of metals, for M′, include Al, Ga and Fe. Preferably, M′is a trivalent cation, e.g. Al. Preferably, the LDH will be a Li-Al, aMg-Al or a Ca-Al AMO-LDH.

The anion X^(n+) in the LDH is any appropriate inorganic or organicanion. Examples of anions that may be used, as X^(n+), in the AMO-LDHinclude carbonate, nitrate, borate, sulphate, phosphate and halide (F⁻,Cl⁻, Br, I⁻) anions. Preferably, the anion X^(n−) is selected from CO₃²⁻, NO₃ and Cl⁻.

The AMO-solvent is any aqueous miscible organic solvent, preferably asolvent which is 100% miscible with water. Examples of suitablewater-miscible organic solvents for use in the present invention includeone or more of acetone, acetonitrile, dimethylformamide,dimethylsulfoxide, dioxane, ethanol, methanol, n-propanol, isopropanol,or tetrahydrofuran. Preferably, the AMO-solvent is selected fromacetone, methanol and ethanol, with ethanol or acetone being the mostpreferred solvent.

According to one preferred embodiment, the layered double hydroxides arethose having the general formula I above

-   in which M is a divalent metal cation;-   M′ is a trivalent metal cation; and-   c is a number from 0.01 to 10, preferably >0.01 and <10, which gives    compounds optionally hydrated with a stoichiometric amount or a    non-stoichiometric amount of water and/or an aqueous-miscible    organic solvent (AMO-solvent), such as ethanol or acetone.

Preferably, in the AMO-LDH of the above formula, M is Mg or Ca and M′ isAl. The counter anion X^(n−) is typically selected from CO₃ ²⁻, OH⁻,F⁻,Cl⁻, Br, I⁻, SO₄ ²⁻, NO₃− and PO₄ ³⁻. Preferably, the LDH will be onewherein M is Mg, M′ is Al and X^(n−) is CO₃ ²⁻.

In carrying out the method of preparing the SiO₂@AMO-LDHs, typically theSiO₂ microspheres are dispersed in an aqueous solution containing thedesired anion salt, for example Na₂CO₃. A metal precursor solution, i.e.a solution combining the required monovalent or divalent metal cationsand the required trivalent cations may then be added, preferablydrop-wise, into the dispersion of the SiO₂ microspheres. Preferably, theaddition of the metal precursor solution is carried out under stirring.The pH of the reaction solution is preferably controlled within the pHrange 8 to 11, more preferably 9 to 10. At pH 9 AMO-LDH nanosheets areattached to the surface of the SiO₂ microspheres. When pH was adjustedto 10, it is clearly observed that a uniform layer of LDH nanosheets ishomogeneously grown on the surface of the microspheres with hierarchaltexture. The AMO-LDH layer thickness achieved at pH 10 is typically80-110 nm. Increasing the pH to 11 also shows full coverage of thesurface with AMO-LDH nanosheets. Furthermore, an increase in pH from 9to 11 demonstrates that the SiO₂ microspheres begin to dissolve,progressing from solid SiO₂ microspheres (core-shell) at pH 9 toyolk-shell spheres at pH 10 to hollow shell spheres at pH 11. Typically,NaOH may be used to adjust the pH of the solution.

In an embodiment, the method of the present invention does not includeammonia.

In a preferred embodiment, the silica-layered double hydroxidemicrospheres have specific surface area of at least 100 m²/g, preferablyat least 177 m²/g, preferably at least 177 m²/g, and more preferably atleast 200 m²/g, and even more preferably at least 250 m²/g.

Suitably, the solid silica-layered double hydroxide microspheres havespecific surface area of at least 100 m²/g.

Suitably, the yolk-shell silica-layered double hydroxide microsphereshave specific surface area of at least 110 m²/g.

Suitably, the hollow-shell silica-layered double hydroxide microsphereshave specific surface area of at least 130 m²/g.

During the reaction, the AMO-LDH produced from the metal precursorsolution reaction is formed on the SiO₂ surfaces of the microspheres asnanosheets.

The obtained solid product may be collected from the aqueous medium bycentrifugation. Typically, the centrifuged solid may be re-dispersed inwater and then collected again by centrifuge. Preferably, the collectionand re-dispersion steps are repeated twice. In order to obtain a productcontaining AMO-solvent, the material obtained after thecentrifugation/re-dispersion procedure described above is washed with,and preferably also re-dispersed in, the desired solvent, for instanceethanol or acetone. If re-dispersion is employed, the dispersion ispreferably stirred. Stirring for more than 2 hours in the solvent ispreferable. The final product may then be collected from the solvent andthen dried, typically in an oven for several hours.

In an embodiment, the LDH is formed in situ. Suitably, the LDH is formedand coated onto the silica microspheres in situ.

The growth of AMO-LDH nanosheets on the surface of the SiO₂ microspheresis “tuneable”. That is to say, by varying the chemistry of the precursorsolution and the process conditions, for instance the pH of the reactionmedium, temperature of the reaction and the rate of addition of theprecursor solution to the dispersion of SiO₂ microspheres, the extentof, and the length and/or thickness of, the AMO-LDH nanosheets formed onthe SiO₂ surface can be varied.

The production of the SiO₂@AMO-LDH microspheres according to theinvention can be carried out as a batch process or, with appropriatereplenishment of reactants, as a continuous process.

The catalyst system of the invention comprises one or more catalytictransition metal complex. By the term “transition metal” it is meant ad-block metal, examples of which include, but are not limited to,zirconium, chromium, titanium and hafnium. The transition metal will becomplexed with one or more ligands, or aromatic or heteroaromatic cycliccompounds to preferably achieve complexes which may be summarized underthe term metallocene. Such aromatic compounds, useful for complexingwith the transition metal, include optionally-substitutedcyclopentadiene, optionally substituted indene andoptionally-substituted pentalene. The aromatic compound used to complexthe transition metal may, further, contain two linked,optionally-substituted cyclopentadiene groups or two linked,optionally-substituted indene and optionally-substituted pentalenegroups. In such linked moieties, the linking group may be provided by alower alkylene group.

Examples of catalysts include known polymerisation catalysts, forexample metallocenes, constrained geometry, Fl complexes and diiminocomplexes.

According to one embodiment of the invention, the transition metalcomplex used in the catalyst system will be selected from

In the formulae shown above, EBI is ethylene bridged indene,2-Me,4-^(Ph)SBI is dimethylsilyl bridged 2-methyl,4-phenylindene,^(nBu)Cp is n-butylcyclopentadiene.

As stated above, the catalyst system of the invention may contain morethan one catalytic transition metal complex.

The catalyst system of the present invention may be made by a processcomprising treating the SiO₂@AMO-LDH, as described above, with at leastone transition metal complex, as described above, having catalyticactivity in the polymerisation of olefins. Typically, the treatment willbe carried out in a slurry of the SiO₂@AMO-LDH in an organic solvent,for example toluene. According to this slurry process, a slurry of theSiO₂@AMO-LDH in, e.g. toluene, is prepared. Separately, a solution ofthe catalytic transition metal complex in, e.g. toluene, is prepared andthen added to the SiO₂@AMO-LDH containing slurry. The resulting combinedmixture is then heated, for instance at 80° C., for a period of time.The solid product may then be filtered from the solvent and dried undervacuum.

Preferably, the SiO₂@AMO-LDH is heat-treated, for instance at 110 to250° C. for a period of time, before it is slurried in the organicsolvent.

Preferably, the SiO₂@AMO-LDH is contacted with an activator, for examplean alkylaluminium activator such as methylaluminoxane, before or afterbeing treated with the catalytic transition metal complex. Typically,methylaluminoxane is dissolved in a solvent, e.g. toluene, and theresulting solution is added to a slurry of calcined SiO₂@AMO-LDH. Theslurry may then be heated, for instance at 80° C., for 1-3 h prior tobeing filtered from the solvent and dried. According to a preferredembodiment, the SiO_(2 @) AMO-LDH is treated with methylaluminoxanebefore being treated with a solution of the catalytic material.

The catalytic compounds will be present on the surface of the solidsupport material. For instance, they may be present on the surface as aresult of adsorption, absorption or chemical interactions.

The present invention also provides a process for producing a polymer ofan olefin which comprises contacting the olefin with a catalyst systemaccording to the invention, as described above.

Thus, as discussed hereinbefore, the present invention also provides theuse of a composition defined herein as a polymerization catalyst, inparticular a polyethylene polymerization catalyst.

In one embodiment, the polyethylene is a homopolymer made frompolymerized ethene monomers.

In another embodiment, the polyethylene is a copolymer made frompolymerized ethene monomers comprising 1-10 wt % of (4-8C) α-olefin (bytotal weight of the monomers). Suitably, the (4-8C) α-olefin is1-butene, 1-hexene, 1-octene, or a mixture thereof.

As discussed hereinbefore, the present invention also provides a processfor forming a polyolefin (e.g. a polyethylene) which comprises reactingolefin monomers in the presence of a composition defined herein.

In another embodiment, the olefin monomers are ethene monomers.

In another embodiment, the olefin monomers are ethene monomerscomprising 1-10 wt % of (4-8C) α-olefin (by total weight of themonomers). Suitably, the (4-8C) α-olefin is 1-butene, 1-hexene,1-octene, or a mixture thereof.

A person skilled in the art of olefin polymerization will be able toselect suitable reaction conditions (e.g. temperature, pressures,reaction times etc.) for such a polymerization reaction. A personskilled in the art will also be able to manipulate the processparameters in order to produce a polyolefin having particularproperties.

In a particular embodiment, the polyolefin is polyethylene.

Particularly Preferred Embodiments

The following represent particular embodiments of the silica-layereddouble hydroxide:

1.1 The Silica-Layered Double Hydroxide Microspheres have the GeneralFormula I

(SiO₂)_(p)@{[M^(z+)_((1−x))M′y+_(x)(OH)₂]^(a+)(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (I)

-   -   wherein,    -   M^(z+) is selected from Li⁺, Ca²⁺, Ni²⁺ or Mg²⁺, and M′^(y+) is        Al³+ or Fe³+;    -   0<x<0.9;    -   b is 0 to 10;    -   c is 0 to 10;    -   p>0,    -   q>0;    -   X^(n−) is selected from carbonate, hydroxide, nitrate, borate,        sulphate, phosphate and halide (F⁻, Cl⁻, Br, I⁻) anions; with        n>0 (preferably 1-5)    -   a=z(1−x)+xy−2; and    -   the AMO-solvent is selected from methanol, ethanol or acetone.        1.2 The Silica-Layered Double Hydroxide Microspheres have the        General Formula I

(SiO₂)_(p)@{[M^(z+)_((1−x))M′y+_(x)(OH)₂]^(a+)(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (I)

-   -   wherein,    -   M^(z+) is selected from Li⁺, Ca²⁺, Ni²⁺ or Mg²⁺, and M′^(y+) is        Al³⁺;    -   0<x<0.9;    -   b is 0 to 10;    -   c is 0 to 10;    -   p>0,    -   q>0;    -   X^(n−) is selected from CO₃ ²⁻, NO₃ ⁻ or Cl⁻; with n>0        (preferably 1-5)    -   a=z(1−x)+xy−2; and    -   the AMO-solvent is ethanol or acetone.        1.3 The Silica-Layered Double Hydroxide Microspheres have the        General Formula Ia

(SiO₂)_(p)@{[M^(z+) _((1−x))Al³⁺_(x)(OH)₂]^(a+)(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (Ia)

-   -   wherein,    -   M^(z+) is selected from Li⁺, Ca²⁺, Ni²⁺ or Mg²⁺;    -   0<x<0.9;    -   b is 0 to 10;    -   c is 0 to 10;    -   p>0,    -   q>0;    -   X^(n−) is selected from CO₃ ²⁻, NO₃ ⁻ or Cl⁻; with n>0        (preferably 1-5)    -   a=z(1−x)+xy−2; and    -   the AMO-solvent is ethanol or acetone.        1.4 The Silica-Layered Double Hydroxide Microspheres have the        General Formula Ia

(SiO₂)_(p)@{[M²⁺ _((1−x))Al³⁺_(x)(OH)₂]^(a+)(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (Ia)

-   -   wherein,    -   0<x<0.9;    -   b is 0 to 10;    -   c is 0 to 10;    -   p>0,    -   q>0;    -   X^(n−) is selected from CO₃ ²⁻, NO₃ ⁻ or Cl⁻; with n>0        (preferably 1-5)    -   a=z(1−x)+xy−2; and    -   the AMO-solvent is ethanol or acetone.        1.5 The Silica-Layered Double Hydroxide Microspheres have the        General Formula Ib

(SiO₂)_(p)@{[Mg²⁺ _((1−x))Al³⁺ _(x)(OH)₂]^(a+)(CO₃²)_(a/n)bH2O·c(ethanol/acetone)}_(q)   (Ib)

-   -   wherein,    -   0<x<0.9;    -   b is 0 to 10;    -   c is 0 to 10;    -   p>0,    -   q>0;    -   a=z(1 -x)+xy−2.        The following represent particular embodiments of the catalyst        system:        2.1 The Catalyst System Comprises a Solid Support Material        Having, on its Surface, One or More Catalytic Transition Metal        Complexes Selected from:

-   -   wherein the solid support material comprises SiO₂@AMO-LDH        microspheres having the formula I

(SiO₂)_(p)@{[M^(z+) _((1−x))M′^(y+)_(x)(OH)₂]¹⁺(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (I)

-   -   wherein,    -   M^(z+) is selected from Li⁺, Ca²⁺, Ni²⁺ or Mg²⁺, and M′^(y+) is        Al³⁺ or Fe³⁺;    -   0<x <0.9;    -   b is 0 to 10;    -   c is 0 to 10;    -   p>0,    -   q>0;    -   X^(n−) is selected from carbonate, hydroxide, nitrate, borate,        sulphate, phosphate and halide (F⁻, Cl⁻, Br, I⁻) anions; with        n>0 (preferably 1-5)    -   a=z(1−x)+xy−2; and    -   the AMO-solvent is selected from methanol, ethanol or acetone.        2.2 The Catalyst System Comprises a Solid Support Material        Having, on its Surface, One or More Catalytic Transition Metal        Complexes Selected from:

-   -   wherein the solid support material comprises SiO₂@AMO-LDH        microspheres having the formula I

(SiO₂)_(p)@{[M^(z+) _((1−x))Al³⁺_(x)(OH)₂]^(a+)(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (Ia)

-   -   wherein,    -   M^(z+) is selected from Li⁺, Ca²⁺, Ni²⁺ or Mg²⁺;    -   0<x<0.9;    -   b is 0 to 10;    -   c is 0 to 10;    -   p>0,    -   q>0;    -   X^(n−) is selected from CO₃ ²⁻, NO₃− or Cl⁻; with n>0        (preferably 1-5)    -   a=z(1−x)+xy−2; and    -   the AMO-solvent is ethanol or acetone.

Preferred, suitable, and optional features of any one particular aspectof the present invention are also preferred, suitable, and optionalfeatures of any other aspect.

Experimental Details

Preparation of Silica (SiO₂) Nanoparticles

Stöber method. The monodispersed silica spheres were synthesised usingthe Stöber method. Tetraethyl orthosilicate (TEOS) (amounts shown below)was added to a mixed solution of ammonia (35 wt %), deionised water andethanol. The white suspension was left to stir vigorously for 17 h. Thevolume of deionised water and ethanol remained constant (30 mL and 50mL, respectively). The volume of TEOS and ammonia was varied to achievethe desired size of silica sphere (13.7 mL, 9.15 mL and 3 mL of TEOSwith 15 mL, 10 mL and 5 mL of ammonia for 800 nm, 550 nm and 300 nmsilica spheres, respectively). The final solid was washed with ethanoland water, until washings were pH 7, followed by drying under vacuumovernight.

Seeded Growth Method. Seeded growth is a two-stage synthesis. The firststage prepares the ‘seeds’. TEOS (1 mL) diluted in ethanol (4 mL), wasadded to a mixed solution of ammonia (10 mL, 35 wt %) and ethanol (46mL) and left to stir vigorously for 2 h. Keeping the reaction conditionsthe same for the second stage of synthesis, the calculated amount ofTEOS diluted in 4× volume of ethanol was added to the seed suspension ata rate of 6 mL/h. After all the TEOS was added the reaction was left tostir for a further 2 h to make sure the particles had reached theirfinal size. The final solid was washed with ethanol (240 mL) and driedunder vacuum overnight.

Preparation of silica@LDH nanoparticles (SiO₂@AMO-LDH). The silica@LDHparticles were synthesised via the coprecipitation method. Silicaspheres (100 mg) were dispersed in deionised water (20 mL) usingultrasound treatment. After 30 min, the desired anion salt (0.96 mmol),Na₂CO₃, was added to the solution and a further 5 min of sonication wascarried out to form solution A. Next an aqueous solution (19.2 mL)containing M²⁺(NO₃)₂·6H₂O (0.96 mmol) (M²⁺=Mg, Ni) and M³⁺(NO₃)₃·9H₂O(0.48 mmol) (M³⁺=Al, Fe) was added at a rate of 60 mL/h to solutionunder vigorous stirring. The pH of the reaction solution was controlledwith the addition of 1 M NaOH by an autotitrator, or was pre-set by the‘Ammonia method’, where ammonia (0.8 mL, 35 wt %) was added at thebeginning of the reaction. The obtained solid was collected withcentrifugation at 4000 rpm for 5 min and then re-dispersed in deionisedwater (40 mL) and stirred for 1 h. The collection and re-dispersion wasrepeated twice. The suspension was then dried under vacuum for materialscharacterisation.

Aqueous Miscible Organic Solvent Treatment. For the AMOST method, thesilica@AMO-LDHs are initially formed using the previous procedures.However, before final isolation, the solid was washed with acetone (40mL) and then re-dispersed in acetone (40 mL) and left to stir overnight.The suspension was then dried under vacuum for materialscharacterisation.

Silica@AMO-LDH (SiO₂@AMO-LDH) Characterisation. Silica@AMO-LDHssynthesised at room temperature with different pHs. Si NMR: pH 10:δ(ppm)−108 (s), −99 (s), −86 (s); pH 11:δ (ppm)−135−−75. Al NMR: pH 10:δ(ppm) 9.6 (s), 61 (s); pH 11:9.2 (s), 56 (s). Silica@AMO-LDHssynthesised at pH 10 at different temperatures. Si NMR: roomtemperature: δ (ppm)−108 (s), −99 (s), −86 (s); 40° C.: δ (ppm)−135−−75.Al NMR: room temperature: δ (ppm) 9.6 (s), 61 (s); 40° C:9.2 (s), 56(s). Silica@AMO-LDHs synthesised with the AMOST method at roomtemperature and pH 10. Si NMR: δ (ppm)31 110 (s), −101 (s), −87 (s). AlNMR:δ (ppm) 9.4 (s), 55 (s).

Silica@AMO-LDH and AMO-LDH as Catalyst Supports. The silica@AMO-LDH usedas a catalyst support contained a silica core (SiO₂) (550 nm) preparedvia the seeded growth method and an LDH layer (Mg/Al 2:1 with CO₃ ²⁻anion) grown at pH 10 at room temperature which was treated with theAMOST method. The AMO-LDH used for comparison was an LDH (Mg/Al 2:1 withCO₃ ²⁻ anion) synthesised under the same conditions and was treated withthe AMOST method. Silica@AMO-LDH and AMO-LDH samples were thermallytreated at 150° C. for 6 h under vacuum (10⁻² mbar). Two equivalents ofthermally treated silica@AMO-LDH (750 mg) and one equivalent ofmethylaluminoxane (375 mg) were heated in toluene (40 mL) at 80° C. for2 h, with swirling to the reaction every 10 minutes. The solvent wasthen removed under vacuum and the colourless solid dried in vacuo for 4h to afford silica@AMO-LDH/MAO, yield: 89%. Similar process was carriedout with the AMO-LDH, yield 84%. Finally, one equivalent ofsilica@AMO-LDH/MAO (500 mg) and 0.01 equivalent of yellow [(EBl)ZrCl₂](12 mg) were heated in toluene (25 mL) at 80° C. for 2 h, with swirlingto the reaction every 10 minutes. The reaction mixture was then left tocool and the solid was allowed to settle. The solid went from colourlessto orange in colour, and the solution was left colourless. The solventwas then removed under vacuum and dried in vacuo for 4 h to affordsilica@AMO-LDH/MAO-[(EBI)ZrCl_(2]) yield: 89%. The same process wascarried out with the AMO-LDH/MAO-[(EBI)ZrCl₂], yield: 93%. EthylenePolymerisation Studies. The catalysts were tested for their ability toact as a catalyst for ethylene polymerisation under slurry conditions inthe presence of TIBA ([TIBA]₀/[Zr]₀=1000). The reactions were performedwith ethylene (2 bar) in a 200 mL ampoule, with the catalyst precursor(10 mg) suspended in hexane (50 mL). The reactions were run for 15-120minutes at 50-90° C. controlled by heating in an oil bath. Thepolyethylene product was washed with pentane (3×50 mL) and the resultingpolyethylene was filtered through a sintered glass frit.

The polymerisation activity of the catalyst supported metallocenecomplexes plotted against temperature is shown in FIG. 1.

FIG. 1 Polymerisation activities of the catalyst supported metallocenecomplexes at temperatures from 50 to 90° C. (a) AMO-LDH/MAO-[(EBI)ZrCl₂]and (b) silica@AMO-LDH/MAO-[(EBI)ZrCl₂]. Polymerisation conditions: 50mL Hexane, 2 bar Ethylene, 1 h, [TIBA]₀/[Zr]₀=1000.AMO-LDH/MAO-[(EBI)ZrCl₂] (a) shows a bell-shaped activity curve, typicalfor the immobilised [EBI(ZrCl₂)], with the optimum temperature forpolymerisation to be found between 70 and 80° C. (activity of 702kg_(PE)/molz_(r)/h/bar at 80° C.), FIG. 1. The curve can be explained bythe increase of the propagation rate with temperature, followed by thetermination rate increasing after the optimum temperature. At 80° C.,when silica@AMO-LDH/MAO-[(EBI)ZrCl₂] was used, the activity is 3.5 timeshigher, 2494 kgPE/molzr/h/bar, than the activity of theAMO-LDH/MAO-[(EBI)ZrCl₂]. The activities of this catalyst are very highon the Gibson scale. Above these temperatures we see a sharp drop in theactivity of the complexes, as is expected as the rate of deactivationincreases. This significant result demonstrates the advantage of thehierarchical structure; growing the LDH on the surface of silica sphereshas resulted in a more active catalyst support.

TABLE 1 Polymerisation data demonstrating the molecular weights (M_(w))and polydispersities (M_(w)/M_(n)) with Temperature varying from 50 to90° C. for 1 h using silica@AMO-LDH/MAO-[(EBI)ZrCl₂] Temperature (° C.)M_(w) (g/mol) M_(w)/M_(n) 50 198251 5.60 60 171780 4.87 70 152496 4.9980 100322 4.10 90 84265 3.93

TABLE 2 Polymerisation data demonstrating the molecular weights (M_(w))and polydispersities (M_(w)/M_(n)) with Temperature varying from 50 to90° C. for 1 h using AMO-LDH/MAO-[(EBI)ZrCl₂] Temperature (° C.) M_(w)(g/mol) M_(w)/M_(n) 50 276454 5.33 60 189953 5.09 70 150138 4.70 80105312 4.96

FIG. 2 Polymerisation activities of the catalyst supported metallocenecomplexes at times from 0 to 120 minutes. (a) AMO-LDH/MAO-[(EBI)ZrCl2]and (b) silica@AMO-LDH/MAO-[(EBI)ZrCl₂]. Polymerisation conditions: 50mL Hexane, 2 bar Ethylene, 1 h, [TIBA]₀/[Zr]₀.

The silica@AMO-LDH and AMO-LDH supported metallocene complexes have beenevaluated for ethylene polymerisation over a timescale of 0-120 minutes,at 70° C., FIG. 2. AMO-LDH/MAO-[(EBI)ZrCl₂] (a) shows an initialincrease in activity reaching a maximum at 15 min, 899kg_(PE)/molz_(r)/h/bar, FIG. 2. After this point, there is a drop inactivity, it appears that AMO-LDH/MAO-[(EBI)ZrCl₂] is over its peak inactivity and has approximately settled to the diffusion controlledlimit. This can be explained by the rapidly increasing amounts ofpolyethylene in the polymerising medium that can hinder the interactionof the catalyst support with the ethylene.Silica@AMO-LDH/MAO-[(EBI)ZrCl₂] (b) shows a similar pattern toAMO-LDH/MAO-[(EBI)ZrCl₂], FIG. 2. The optimum time for polymerisation isagain 15 min with the activity reaching 2406 kg_(PE)/molz_(r)/h/bar, 2.5times higher than AMO-LDH at the same time. The curves are expected tolevel off completely as the diffusion control limit is reached.

TABLE 3 Polymerisation data demonstrating the molecular weights (M_(w))and polydispersities (M_(w)/M_(n)) with Time varying from 0 to 120minutes at 70° C. using silica@AMO-LDH/MAO-[(EBI)ZrCl₂] Time (minutes)M_(w) (g/mol) M_(w)/M_(n) 15 143088 4.12 30 137341 4.69 60 152496 4.99120 147827 4.57

TABLE 4 Polymerisation data demonstrating the molecular weights (M_(w))and polydispersities (M_(w)/M_(n)) with Time varying from 0 to 120minutes at 70° C. using AMO-LDH/MAO-[(EBI)ZrCl₂] Time (minutes) M_(w)(g/mol) M_(w)/M_(n) 5 175468 4.15 15 194344 4.51 30 171280 4.30 60150138 4.70 120 144305 5.82

After 15 minutes of polymerisation (a) small spherical particles withinthe range 0.6-1.4 μm are present within the sample. These particlesappear to be aggregated together. Strings of growing polymer can beseen. After 1 h, the polymer size and morphology is still not uniform(2.8-3.4 μm).

FIG. 3 SEM images of polymer produced using the silica@AMO-LDHmetallocene catalyst support complex after (a) 15 min and (b) 1 h. (c)Silica@LDH.

In FIG. 3, the silica@AMO-LDH metallocene catalyst issilica@AMO-LDH/MAO-[(EBI)ZrCl₂]. Image (a) shows the polyethyleneparticles produced after 15 minutes. Spherical polymer particles 1.3-1.9μm are present in the sample along with larger 6.3-10.3 μm particles.The polymer has mirrored the catalyst support morphology to a certainextent; the original silica@AMO-LDH is shown in image (c). After 1 h (b)the individual polymer particles have grown and aggregated togetherforming a very large polymer particle of 27 μm.

FIG. 4. XRD patterns of SiO₂@LDH microspheres prepared according toexample 1 (a) conventional water washing (b) acetone washing.

FIG. 5. TEM image of SiO₂@LDH microspheres with different morphology (a)solid (example 1), (b) yolk-shell (example 1 at 40° C.) and (c) hollow(example 1 at pH 11).

FIG. 6 TEM image of SiO₂@AMO LDH microspheres according to examples 5and 7 at pH=10 and room temperature (a) Mg:Al=3:1 (b)Mg:Al:Fe=3:0.9:0.1.

FIG. 7 TEM image of SiO₂@AMO-LDH with Mg:Ni:Al=2.7:0.3:1 microsphereswith different morphology according to example 6 (a) pH=10 and roomtemperature (b) pH=10 and 40° C. (c) pH=11 and 40° C.

Further, non-limiting, examples of SiO₂@AMO-LDHs suitable for use in thepresent invention are detailed below:

EXAMPLE 1

Silica spheres (100 mg, 550 nm) were dispersed in deionised water (20mL) using ultrasound treatment. After 30 min., Na₂CO₃ (0.96 mmol) wasadded to the solution and a further 5 min of sonication was carried outto form solution A. Next an aqueous solution (19.2 mL) containingMg(NO₃)₂·6H₂O (0.96 mmol) and Al(NO₃)₃·9H₂O (0.48 mmol) was added at arate of 60 mL/h to solution A under vigorous stirring at roomtemperature. The pH of the reaction solution was controlled to be 10with the addition of 1 M NaOH. The obtained solid was collected withcentrifugation at 4000 rpm for 5 min and then re-dispersed in deionisedwater (40 mL) and stirred for 1 h. The collection and re-dispersion wererepeated twice. Afterward, the solid was washed with acetone (40 mL) andthen re-dispersed in acetone (40 mL) and left to stir overnight. Thesolid was then dried under vacuum.

The SiO₂@LDH obtained in this Example, before the treatment withacetone, has the formula:

(SiO₂)_(0.04)@{[Mg_(0.75) Al_(0.25)(OH)₂](CO₃)_(0.125)·1.34(H₂O)}_(0.05)

The SiO₂@AMO-LDH, obtained after acetone treatment, has the formula:

(SiO₂)_(0.04)@{[Mg_(0.75)Al_(0.25)(OH)₂](CO₃)_(0.125)·0.29(H₂O)·0.15(acetone)}_(0.05)

Yolk shell particles were obtained by carrying out the addition of theaqueous solution containing the Mg(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O at 40°C. and pH10.

Hollow shell particles were obtained by carrying out the addition of theaqueous solution containing Mg(NO₃)₂·6H₂O and Al(NO₃)₃·9H₂O at roomtemperature but at pH11.

Surface Area Analysis

The solid SiO₂@LDH, the yolk shell SiO₂@LDH and the hollow shellSiO₂@LDH prepared as described above but without acetone treatment weresubjected to Brunauer-Emmett-Teller (BET) surface area analysis.

The N₂ BET surface areas of the products were:

BET surface area (m²g⁻¹) Solid (i.e. core-shell) SiO₂@LDH 107 Yolk-shellSiO₂@LDH 118 Hollow-shell SiO₂@LDH 177

The BET surface areas reported above may be favourably compared to thoseof SiO₂@LDHs prepared according to (A) Shao et al. Chem. Mater. 2012,24, pages 1192-1197 and to those of SiO₂@LDHs prepared according to (B)Chen et al. J. Mater. Chem. A, 1, 3877-3880.

BET surface area (m²g⁻¹) (A) SiO₂ microspheres pre-treated with Al(OOH).Product SiO₂@NiAl LDH. Solid (i.e. core-shell) SiO₂ microspheres 42.3Yolk-shell SiO₂@LDH microspheres 68 Hollow-shell SiO₂@LDH microspheres124 (B) SiO₂ microspheres - no pre-treatment - ammonia method. ProductSiO₂@LDH. Solid (i.e. core-shell) SiO₂@LDH microspheres 61

Core-shell SiO₂@LDHs were prepared according to the procedures describedin Example 1 and in the Examples 2 and 3 below having differentthicknesses of LDH layer. The ratio of Mg/Al was varied to control thethickness of the LDH layer. A Mg:Al ratio of 1:1 was found to give anLDH layer of thickness 65 nm, a ratio of 2:1 was found to give an LDHlayer of thickness 110 nm and a layer of thickness of 160 nm wasobtained using a Mg:Al ratio of 3:1. TEM images are shown in FIG. 15.Core-shell SiO₂@LDHs were also prepared according to the proceduredescribed in Example 1 above using different sized SiO₂ microspheres,300 nm, 550 nm and 800 nm. TEM images are shown in FIG. 16. TEM imagesof the SiO₂@LDHs produced with different morphology (a) solid (Example1), (b) yolk shell (Example 1 at 40° C.) and (c) hollow (Example 1 atpH11), as described above, are shown in FIG. 17.

EXAMPLE 2

In order to obtain a 1:1 Mg:Al LDH, the procedure described above inExample 1 was repeated with the exception that an aqueous solution (19.2mL) containing Mg(NO₃)₂·6H₂O (0.72 mmol) and Al(NO₃)₃·9H₂O (0.72 mmol)was added at a rate of 60 mL/h to solution A under vigorous stirring.

EXAMPLE 3

In order to obtain a 3:1 Mg:Al LDH, the procedure described above inExample 1 was repeated with the exception that an aqueous solution (19.2mL) containing Mg(NO₃)₂·6H₂O (1.08 mmol) and Al(NO₃)₃·9H₂O (0.36 mmol)was added at a rate of 60 mL/h to solution A under vigorous stirring.The XRD patterns of the SiO₂@LDH samples prepared with Mg:Al ratios of1:1 (Example 2) and 3:1 (Example 3) are shown in FIG. 12.

EXAMPLE 4

The silica@LDH particles were synthesised via the coprecipation method.Silica spheres (100 mg, 550 nm) were dispersed in deionised water (20mL) using ultrasound treatment. After 30 min, the anion salt (0.96mmol), Na₂CO₃, was added to the solution containing ammonia (0.8 mL,35%) and a further 5 min of sonication was carried out to form solutionA. Next an aqueous solution (19.2 mL) containing Mg(NO₃)₂·6H₂O) (0.96mmol) and Al(NO₃)₃·9H₂O (0.48 mmol) was added at a rate of 60 mL/h tosolution A under vigorous stirring. The obtained solid was collectedwith centrifugation at 4000 rpm for 5 min and then re-dispersed indeionised water (40 mL) and stirred for 1 h. The collection andre-dispersion were repeated twice. Afterward, the solid was washed withacetone (40 mL) and then re-dispersed in acetone (40 mL) and left tostir overnight. The solid was then dried under vacuum. The suspensionwas then dried under vacuum for materials characterisation.

-   -   The features disclosed in the foregoing description, in the        claims as well as in the accompanying drawings, may both        separately and in any combination thereof be material for        realizing the invention in diverse forms thereof.

EXAMPLE 5

In order to obtain Silica@AMO-LDHs in Mg:Al=3:1. Synthesise theSilica@LDH particles by using the co-precipitation method, dispersesilica spheres (100 mg) in the deionised water (20 mL) by usingultrasound treatment for 30 min, add the anion salt Na₂CO₃ (0.96 mmol)in the solution and further treat by ultrasound for 5 min, the finallysolution named A. Then add an aqueous solution (19.2 mL) containing(1.08 mmol) Mg²⁺ and (0.36 mmol) Al³⁺ in the solution A at the rate of60 mL/h with vigorous stirring. The pH of the reaction solution iscontrolled with the addition of 1 M NaOH by an autotitrator. And themorphology of Silica@LDH is controlled by pH and temperature. Theobtained solid is collected with centrifugation at 5000 rpm for 5 minand then re-dispersed in deionised water (40 mL) and stir for 1 h, thewashing need repeated twice. Before final isolation, the solid is washedwith acetone (40 mL) and left to stir over night, and the suspension isthen dried under vacuum

EXAMPLE 6

In order to obtain Silica@AMO-LDHs in Mg:Ni:Al=2.7:0.3:1. The Silica@LDHparticles will be synthesized by using the co-precipitation method,disperse silica spheres (100 mg) in the deionised water (20 mL) by usingultrasound treatment for 30 min, add the anion salt Na₂CO₃ (0.96 mmol)in the solution and further treat by ultrasound for 5 min, the finallysolution named A. Then add an aqueous solution (19.2 mL) containing(0.972 mmol) Mg²⁺, (0.108 mmol) Ni²⁺ and (0.36 mmol) Al³⁺ in thesolution A at the rate of 60 mL/h with vigorous stirring. The pH of thereaction solution is controlled with the addition of 1 M NaOH by anautotitrator. As followed the morphology of Silica@LDH is controlled bypH and temperature. The obtained solid is collected with centrifugationat 5000 rpm for 5 min and then re-dispersed in deionised water (40 mL)and stir for 1 h, the washing need repeated twice. Before finalisolation, the solid is washed with acetone (40 mL) and left to stirover night, and the suspension is then dried under vacuum.

EXAMPLE 7

In order to obtain Silica@AMO-LDHs in Mg:Al:Fe=3:0.9:0.1. The Silica@LDHparticles synthesise using the co-precipitation method, disperse silicaspheres (100 mg) in the deionised water (20 mL) by using ultrasoundtreatment for 30 min, add the anion salt Na₂CO₃ (0.96 mmol) in thesolution and further treat by ultrasound for 5 min, the finally solutionnamed A. Then add an aqueous solution (19.2 mL) containing (1.08 mmol)Mg²⁺, (0.324 mmol) Al³⁺ and (0.036 mmol) Fe³⁺ in the solution A at therate of 60 mL/h with vigorous stirring. The pH of the reaction solutionis controlled with the addition of 1 M NaOH by an autotitrator. Asfollowed the morphology of Silica@LDH is controlled by pH andtemperature. The obtained solid is collected with centrifugation at 5000rpm for 5 min and then re-dispersed in deionised water (40 mL) and stirfor 1 h, the washing need repeated twice. Before final isolation, thesolid is washed with acetone (40 mL) and left to stir over night, andthe suspension is then dried under vacuum

-   -   The features disclosed in the foregoing description, in the        claims and in the accompanying drawings may, both separately and        in any combination thereof, be material for realizing the        invention in diverse forms thereof.

1. A catalyst system comprising a solid support material having, on itssurface, one or more catalytic transition metal complex wherein thesolid support material comprises SiO₂@AMO-LDH microspheres having theformula I(SiO₂)_(p)@{[M^(z+) _((1−x))M′^(y+)_(x)(OH)₂]^(a+)(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q) wherein, M′ andM′Y⁺ are two different charged metal cations; z=1 or 2; y=3 or 4;0<x<0.9; b is 0 to 10; c is 0.01 to 10, preferably >0.01 and <10; p>0;q>0; X^(n−) is an anion with n>0; a=z(1−x)+xy−2; and the AMO-solvent isan 100% aqueous miscible organic solvent.
 2. The catalyst systemaccording to claim 1, wherein the solid support material has the formulaI in which M′ is one or more trivalent metal cations.
 3. The catalystsystem according to claim 1, wherein the solid support material has theformula I in which M is one or more divalent cation (e.g. Mg or Ca). 4.The catalyst system according to claim 1, wherein the solid supportmaterial has the formula I in which X^(n−) is selected from CO₃ ²⁻, OH⁻,F , Cl⁻, Br⁻, I⁻, SO²⁻, NO₃− and PO₄ ³⁻, or a mixture thereof.
 5. Thecatalyst system according to claim 1, wherein the solid support materialhas the formula I in which M is Mg, M′ is Al and X^(n−) is CO₃ ⁻.
 6. Thecatalyst system according to claim 1, wherein the solid support materialhas the formula I in which AMO-solvent is ethanol, acetone or methanol.7. The catalyst system according to claim 1, wherein the catalytictransition metal complex is at least one complex of a metal selectedfrom zirconium, iron, chromium, cobalt, nickel, titanium and hafnium,the complex containing one or more aromatic or heteroaromatic ligands.8. The catalyst system according to, wherein the catalytic transitionmetal complex is a metallocene containing zirconium or hafnium.
 9. Thecatalyst system according to claim 1, wherein the catalytic transitionmetal complex is at least one compound selected from


10. The catalyst system according to claim 1, wherein the system isobtainable by a process comprising the step of activating the solidsupport material with an alkylaluminoxane Of triisobutylaluminium(TIBA), triethylaluminium (TEA) or diethylaluminium chloride (DEAC). 11.The catalyst system according to claim 10, wherein the alkylaluminoxaneis methylaluminoxane (MAO) or modified methylaluminoxane (MMAO).
 12. Amethod of making the catalyst system of claim 1 which comprises (a)providing a solid support material comprising SiO₂@AMO-LDH microsphereshaving the formula (I)(SiO₂)_(p)@{[M^(z+) _((1−x))M′^(y+)_(x)(OH)₂]¹⁺(X^(n−))_(a/n)·bH₂O·c(AMO-solvent)}_(q)   (I) wherein, M′and M′^(y+) are two different charged metal cations; z=1 or 2; y=3 or 4;0<x<0.9; b is 0 to 10; c is 0.01 to 10, preferably c >0.01 and <10; p>0,q>0; X^(n−) is an anion with n>0; a=z(1−x)+xy−2; and the AMO-solvent isan aqueous miscible organic solvent, (b) treating the SiO₂@AMO-LDHmicrospheres with at least one catalytic transition metal complex havingolefin polymerisation catalytic activity.
 13. The method according toclaim 12, wherein the solid support material has the formula I in whichM′ is one or more trivalent metal cations.
 14. The method according toclaim 12, wherein the solid support material has the formula I in whichM is one or more divalent metal cations.
 15. The method according toclaim 12, wherein the solid support material has the formula I in whichX^(n−) is selected from CO₃ ²⁻, OH⁻, F, Cl⁻, Br⁻, I⁻, SO²⁻, NO₃− and PO₄³⁻, or a mixture thereof.
 16. The method according to claim 1, whereinthe solid support material has the formula I in which M is Mg, M′ is Aland X^(n−) is CO₃ ⁻.
 17. The method according to claim 12, wherein thesolid support material has the formula I in which AMO-solvent isethanol, acetone or methanol.
 18. The method according to claims 12,wherein the catalytic transition metal complex is at least one complexof a metal selected from zirconium, iron, chromium, cobalt, nickel,titanium and hafnium, the complex containing one or more aromatic orheteroaromatic ligands.
 19. The method according to claim 12, whereinthe catalytic transition metal complex is a metallocene containingzirconium or hafnium.
 20. The method according to claim 12, wherein thecatalytic transition metal complex is at least one compound selectedfrom


21. The method according to claim 12, further comprising a step ofcalcining the SiO₂@AMO-LDH microspheres, before the treating step (b).22. The method according to claim 21, further comprising a step oftreating the calcined SiO₂@AMO-LDH with an alkylaluminoxane before thetreating step (b).
 23. The method according to claim 22, wherein thealkylaluminoxane is methylaluminoxane (MAO) or modifiedmethylaluminoxane (MMAO).
 24. (canceled)
 25. (canceled)
 26. A processfor forming a polyethylene homopolymer or a polyethylene copolymer whichcomprises reacting olefin monomers in the presence of a system accordingto claim
 1. 27. A process for producing a polymer of an olefin whichcomprises contacting the olefin with the solid catalyst system accordingto claim
 1. 28. The process according to claim 27, wherein the olefin isethylene.
 29. The process according to claim 27, wherein the process isperformed at a temperature of 50-100° C.
 30. The use according to claim26, wherein the copolymer comprises 1-10 wt % of a (4-8C) α-olefin.